The present invention relates to spin-transfer torque magnetoresistive random access memory (STT-MRAM devices), and more specifically, to encapsulating a magneto-resistive random access memory (MRAM) device using silicon-rich silicon nitride film.
A spin-transfer torque magnetoresistive random access memory device is a type of solid state, non-volatile memory that uses tunneling magnetoresistance (TMR or MR) to store information. MRAM includes an electrically connected array of magnetoresistive memory elements, referred to as magnetic tunnel junctions (MTJs). Each magnetic tunnel junction includes a free layer and fixed/reference layer that each includes a magnetic material layer. A non-magnetic insulating tunnel barrier separates the free and fixed/reference layers. The free layer and the reference layer are magnetically de-coupled by the tunnel barrier. The free layer has a variable magnetization direction, and the reference layer has an invariable magnetization direction.
A magnetic tunnel junction stores information by switching the magnetization state of the free layer. When magnetization direction of the free layer is parallel to the magnetization direction of the reference layer, the magnetic tunnel junction is in a low resistance state. Conversely, when the magnetization direction of the free layer is antiparallel to the magnetization direction of the reference layer, the magnetic tunnel junction is in a high resistance state. The difference in resistance of the magnetic tunnel junction may be used to indicate a logical ‘1’ or ‘0’, thereby storing a bit of information. The TMR of a magnetic tunnel junction determines the difference in resistance between the high and low resistance states. A relatively high difference between the high and low resistance states facilitates read operations in the MRAM.
MRAM devices can be encapsulated after patterning, which may be done to protect the device. Encapsulation, which can be with materials such as silicon nitride or aluminum oxide, may be used to protect the MRAM device from damage in later processing steps.